Fig 1.
The experimental task involved repetitive radial-ulnar deviation movements between target regions in each direction.
In the Pain 5–1 and Pain 5–0 experiments less or no, respectively, noxious stimulation was determined by the alignment of the wrist in the flexion-extension plane (B) as the wrist passed through radial-ulnar deviation neutral (A). The range of variation in the flexion and extension direction was identified in the Baseline condition and one third of this range was selected either in the flexion (*) or extension (#) direction. Movements performed with alignment in the flexion-extension plane in this target region either induced no stimuli or stimuli with reduced intensity. Panel C shows the timeline of the experiment. Max–maximum, dev–deviation, stim–stimulation, reps–repetitions.
Fig 2.
Representative data for the intensity of pain reported with electrical stimulation.
Data are shown for pain rating (11-point numerical rating scale; 0–10) vs. stimulus intensity (0–10 mV) reported by a representative participant from the Pain 5–1 experiment before (white circles) and after the baseline/experimental blocks (black circles). A quadratic function was fitted to the pre-movement data to determine the stimulus intensities required to elicit the desired pain intensity for the painful Experimental block.
Fig 3.
Three analysis measures demonstrated with data from a representative participant.
A. Wrist configuration in the secondary planes (flexion-extension; pronation-supination) is shown for each repetition of movement at the moment the wrist crossed the neutral position in the primary plane (radial-ulnar deviation). Vector length is shown from the mean position in each direction for each entire block. Black–Baseline block; Red–Experimental block B. Vector length between the average configuration of the wrist at the moment it passed the neutral in the primary plane (radial-ulnar deviation) recorded for all repetitions in the Baseline block, and the position of the wrist for each repetition separately of the Experimental block. C. Path length between the wrist positions at the time it passed the neutral in the primary plane (radial-ulnar deviation) during successive repetitions for the Baseline and Experimental block. The large circle represents the start of the block and the box represents the end. In all panels the green box indicates the region of configurations designated to provide no/minimal noxious stimulation based on angle in the flexion-extension plane.
Fig 4.
Group data for change of wrist/forearm alignment, quantified as average vector length relative to mean alignment used in Baseline blocks (refer to Fig 3B).
Group mean and 95% CI of average vector length of 10-repetition epochs for the Control (white), Pain 5–1 (black), and Pain 5–0 (grey) participant groups are shown. *—p<0.05 between bracketed items.
Fig 5.
Group data for movement variability, quantified as with sum of path length during averaged across blocks.
Group mean and 95% CI of sum of path length of 10-repetition epochs for the Control (white), Pain 5–1 (black), and Pain 5–0 (grey) groups. *—p<0.05 between bracketed items.
Fig 6.
Two-dimensional movement maps that depict the three distinct movement strategies used by three separate representative participants in the Pain 5–1 and Pain 5–0 groups who used ‘no overall change, greater use of less noxious stimulation’ (a-c), ‘small change’ (d-f), or ‘large change’ (g-i). In all plots black and red circles/lines depict the Baseline and Experimental blocks, respectively. Plots show forearm pronation-supination angle vs. flexion-extension angle for the 60 repetitions of each block. Separate sub-plots represent different analyses. In the left panels, lines show path length plotted between consecutive repetitions of each block starting with repetition 1 (large triangles) and ending with repetition 60 (large squares). Middle panels show the alignment of the wrist/forearm in the secondary planes for the 60 repetitions relative to the mean alignment (large circles) for each block. Right panels show ‘vector length’ (blue lines) of wrist/forearm alignment in the pain condition relative to the mean alignment of the Baseline block. Note that different scales are used for the axes of the three movement strategies. Scale bars in the bottom left corner of each sub-plot in the right panels represents 5° in each direction (i.e. pronation-supination, flexion-extension). Green shaded areas represent the range of alignments in the flexion-extension direction selected for the less intense noxious stimulus. The three plots for each participant are presented with the same scale.
Table 1.
Data for individual participants for each strategy group.
Fig 7.
Pain reported at the start (first 20 epochs; open circles) and end (last 20 epochs; closed circles) for each strategy and with all strategies combined.
Each strategy led to a reduction in pain, although only the “no change” strategy involved greater use of the range with reduced noxious input. The reduction in pain in the “small” and “large” change strategy was achieved despite no change in noxious input.